Freezing rain and snow tend to accumulate as ice at a rapid rate especially on the wings of aircraft due to the heat capacity of metals used in their construction and the relatively flat surface which facilitates collection and crystallization. The airline industry, through unfortunate experiences, has become well aware of the critical fact that accumulated ice on an aircraft is extremely hazardous at takeoff due to the added weight and detraction from the aerodynamic lift of the wings. Therefore, an important safety factor in winter flight for the commercial airline industry, as well as in military operations, is the removal and prevention of ice formation from the exterior of aircraft.
Because deicing formulations used on aircraft are often ultimately washed into a storm drain system or a waterway, it is important that the composition be nontoxic go the environment, particularly aquatic life. It is also important that such deicing formulations be able to function well in a variety of weather conditions, both as deicer to remove accumulated ice and snow, and as an anti-icer, to prevent ice formation on aircraft. It is further important that such deicing formulations are not slippery; otherwise they could undesirably reduce the traction of the surface for aircraft and other vehicles.
Presently available ethylene glycol-based and methanol-containing commercial deicer formulations for the exterior of aircraft are toxic, corrosive to metals, slippery, and often flammable. Moreover, glycol-containing fluids are known to be damaging to the environment, to resist biological degradation, and to be toxic to humans and other animals.
There remains a need for effective, environmentally acceptable deicing solutions for use on aircraft, particularly wings, which are nontoxic, non-flammable, rapidly and visibly applicable, and essentially noncorrosive to the constructive metals of aircraft.
U.S. Pat. No. 2,233,185 to Smith discloses the use of alkali metal salts of formic, acetic, propionic, and butyric acids as antifreeze compositions and the inclusion of anti-corrosive agents, such as urea, arsenious oxide, chromates, and oils or emulsions, e.g. mineral oil, in such solutions. These solutions are not as effective as desired, and this level of anti-corrosiveness is no longer considered adequate for ordinary long-term use.
U.S. Pat. No. 5,064,551 to Smith discloses aqueous solutions of alkali metal acetates or alkali metal formates as deicing compositions that are alleged to be environmentally friendly and which include metal corrosion inhibitors. Disclosed are acetate and formate solutions which include potassium phosphate, sodium nitrite and EDTA. Although these compositions include some metal corrosion inhibitors, they include environmentally undesirable nitrites, and they are not presently considered to be environmentally acceptable or suitable for use as aircraft surface anti-icers.
It is an object of the present invention to provide effective aircraft surface deicers, particularly suitable for wing deicing, which can be easily applied, act quickly, are nonslippery, and are effective over a wide range of temperatures and weather conditions.